This story appears in the October 2020 issue of National Geographic magazine.
While the human tally of COVID-19 cases has risen, animal cases have remained novelties. As of this moment, you can count the affected species on one hand: lions, tigers, domestic cats, dogs, mink. The pets contracted the virus from their owners; the big cats, likely from an asymptomatic caregiver; and the mink, likely from fur farm workers or possibly other infected animals.
The virus is zoonotic—originating with animals—but causes a fundamentally human disease, says virologist Diego Diel of Cornell University’s Animal Health Diagnostic Center. If the virus that humans are spreading were a significant threat to animal health, he says, we’d know by now.
Beyond that conclusion is a sea of unknowns. There’s no evidence that domesticated animals can pass the virus to humans, but there’s also no widespread animal testing. “Do we test every cat and dog that has respiratory symptoms? Maybe we will be in 12 months,” says microbiologist Shelley Rankin at the University of Pennsylvania School of Veterinary Medicine. “But the only reason we’ve done that in the past has been when there is a direct link to human health.”
Only experimental in-vivo studies, Diel says, could determine how susceptible different species are to contracting, transmitting, or getting sick from this virus.
Tiger, a world first
In April, Nadia, a four-year-old tiger at New York’s Bronx Zoo, became the first non-domesticated animal in the world reported positive for the virus. Four other tigers at the zoo later tested positive. The tigers had coughs; that and wheezing were common animal symptoms.
Cats’ virus risk known
Cats are known to be susceptible to coronaviruses, and several pet cats in Europe, Asia, and the U.S. have tested positive for the virus. All but one belonged to people who had tested positive for COVID-19, the disease the virus causes. The other was an outdoor cat let out in an affected area.
Farms’ mink infected
On several fur farms in the Netherlands, Spain, Denmark, and the U.S., mink tested positive for the virus that causes COVID-19. In response, hundreds of thousands of mink on affected farms in Europe were killed, and the Netherlands is shutting its mink farm industry permanently.
Lions weather virus
Three lions at the Bronx Zoo also tested positive. Veterinary labs at Cornell University, the University of Illinois, and a federal lab confirmed the results by testing fecal samples. All eight lions and tigers are believed to have been infected by an asymptomatic zoo worker and have recovered.